Optical systems used in optical apparatuses such as a projector, a digital camera, a film camera and the like are generally composed of a plurality of optical lenses. The optical lenses need to be fixed to their respective holding barrels such that an optical axis of each lens coincides. However, the optical lenses may be decentered when the holding barrels are processed with poor accuracy or the optical lenses are mounted in the holding barrels with poor precision. As a result, an optical performance of the whole optical system is lowered.
In order to prevent the decentering of the optical lenses, in Japanese patent laid-open publication No. 8-327870, a first holding member which holds a first lens group is provided with projections at a predetermined interval (or a predetermined angle) on its outer peripheral surface, and a second holding member which holds a second lens group is provided with projections at a predetermined interval on its inner peripheral surface. The first holding member is fitted into the second holding member such that the projections of the first holding member contact the projections of the second holding member. When the first lens group is decentered, the first holding member is rotated around an optical axis from the state that the projections of the first and second holding members contacting with each other, and thereby the position of the first holding member is adjusted in a plane perpendicular to the optical axis.
In Japanese patent laid-open publication No. 2002-196204, when a connecting plate fixed to a first holding member which holds a first optical lens, and a second holding member which holds a second optical lens are fixed by using a plurality of screws, each screw is firstly penetrated through one of through holes of the second holding member and through a spring washer. The screw is then threaded into a screw hole of the connecting plate. When the screws are used for a temporary fix, the position of the second holding member is adjusted in a plane perpendicular to an optical axis so as to correct the decentering of the second optical lens. At this time, tilt of the second optical lens held by the second holding member is also adjusted by respectively changing the amount of loosening and tightening of the screws.
However, in the method disclosed in Japanese patent laid-open publication No. 8-327870, the first holding member is attached to the second holding member with contacting each other. When a contact surface of each first and second holding member has low precision, the first lens group held by the first holding member is decentered. Moreover, relative distance from the first lens group to the second lens group changes, and therefore the optical performance of the whole optical system is deteriorated. In the method disclosed in Japanese patent laid-open publication No. 2002-196204, the tilt of the second optical lens is adjusted after the position of the same is adjusted. While changing the amount of loosening the screws, the second holding member may move from the adjusted position in the plane perpendicular to the optical axis. Accordingly, this method is not appropriate for adjusting the decentering of the optical system.